WASHINGTON (Reuters) - The White House budget office said on Wednesday it was probing whether a $43,000 soundproof phone booth installed for Environmental Protection Agency chief Scott Pruitt violated the law, while dozens of Democratic senators called for him to resign over allegations of ethics lapses.

Pruitt has been under fire for potential ethics lapses, including flying first class, excessive spending on security, and the rental of a room in a Washington condominium owned by the wife of an energy lobbyist.

The Office of Management and Budget is reviewing whether spending on the booth installed in Pruitt's office broke a law prohibiting federal agencies from incurring expenses in excess of available funds, known as the Anti-Deficiency Act.

"We take the anti-deficiency statue very, very seriously and if (it's) been broken, we'll follow the rules," Mick Mulvaney, the head of the Office of Management and Budget, told lawmakers in a House hearing. "We will enforce the law, and we'll do so in a transparent fashion."

An OMB spokeswoman said the probe had already begun and her agency was working with the EPA on it.

The EPA's approval of the phone booth violated both the anti-deficiency law and another requiring agencies to notify Congress when they obligate more than $5,000 in federal funds to make improvements in an office of a presidential appointee, the Government Accountability Office, a congressional watchdog, said on Monday.

Pruitt has said the phone booth is necessary for him to conduct official business. When asked about the OMB's probe, Jahan Wilcox, an EPA spokesman, said his agency disagreed that spending on the booth required notification to Congress and said the agency is addressing the GAO's concern.

President Donald Trump said this month that Pruitt, who has carried out his policy of slashing regulations on the fossil fuel industry, "has done a fantastic job." Trump added that he will look into the allegations of ethical lapses.

Mulvaney said the anti-deficiency law is technically a criminal statute, but he did not know if anybody had ever been charged criminally with violating it.

Both Republican and Democratic lawmakers have criticized Pruitt over the allegations. On Wednesday, 38 Democratic U.S. senators and an independent who votes with them in the 100- member chamber introduced a resolution calling for Pruitt to resign.

Pruitt has "completely violated the trust of the American people and the standards of his office, with a list of ethical transgressions that grows longer by the day," Senator Tom Udall said.

The Senate is controlled by Pruitt's fellow Republicans. Although Republicans can defeat the resolution, it is symbolically important because it represents the most senators ever to call for a cabinet member's ouster in such a petition, its sponsors said.

More than 130 U.S. representatives signed a companion resolution in the 435-seat House of Representatives.